Heat exchangers have been known which include a multitude of flat tubes and a header collecting pipe connected to the flat tubes, and in which heat is exchanged between a refrigerant flowing inside the flat tubes and air flowing outside the flat tubes. In the heat exchanger disclosed in Patent Document 1, a multitude of vertically-extending flat tubes are arranged in the horizontal direction, and a header collecting pipe is connected to respective lower ends of the flat tubes. Further, in the heat exchanger disclosed in Patent Document 2, a multitude of horizontally-extending flat tubes are arranged in the vertical direction, and a header collecting pipe is connected to respective end portions of the flat tubes.
A refrigerant supplied to the heat exchanger of this type first flows into the header collecting pipe, and then branches into multiple flows to go into the plurality of flat tubes. When the heat exchanger of this type functions as an evaporator for a refrigerating apparatus, a gas-liquid two-phase refrigerant is supplied to the heat exchanger. That is, in this case, a gas-liquid two-phase refrigerant is distributed to the respective flat tubes through the header collecting pipe.